1. Field of the Invention
The invention relates to a roll stiffness control apparatus of a vehicle. More particularly, the invention relates to a roll stiffness control apparatus of a vehicle, which controls a roll stiffness distribution ratio between front wheels and rear wheels based on a remaining capacity of the front wheels to generate a lateral force and a remaining capacity of the rear wheels to generate a lateral force such that the roll stiffness distribution ratio between the front wheels and the rear wheels is changed to an appropriate value.
2. Description of the Related Art
Japanese Patent Application Publication No. JP(A) 06-211018 discloses a known roll stiffness control apparatus of a vehicle, for example, an automobile. This roll stiffness control apparatus calculates a target yaw rate of a vehicle, and controls a roll stiffness distribution ratio between front wheels and rear wheels such that an actual yaw rate of the vehicle comes closer to the target yaw rate.
With such a roll stiffness control apparatus, the roll stiffness distribution ratio between the front wheels and the rear wheels is controlled such that the actual yaw rate of the vehicle comes closer to the target yaw rate. It is, therefore, possible to improve running stability of the vehicle during cornering without affecting acceleration/deceleration of the vehicle, unlike a case where braking forces/driving forces of the wheels are individually controlled so that the actual yaw rate of the vehicle comes closer to the target yaw rate.
Generally, when the roll stiffness distribution ratio between the front wheels and the rear wheels is controlled, a vertical load ratio between a right wheel and a left wheel changes on each of a front wheel side and a rear wheel side. Accordingly, a longitudinal force and a lateral force which can be generated by each wheel also change, and a turning limit of the vehicle also changes. However, in the above-mentioned conventional type of roll stiffness control apparatus, a force which can be generated by each wheel is not taken into account. Therefore, there is room for improvement in control of the roll stiffness distribution ratio between the front wheels and the rear wheels, which is performed so as to improve the turning limit of the vehicle.